As disclosed in National Publication of International Patent Application No. 10-504397 and others, methods are available in which an analysis object to be tested is disposed in a certain portion on a disc, the analysis object is traced, and an image of the analysis object is obtained by using the reproducing function of the optical disc.
As shown in FIGS. 6 and 7, an optical disc 101 generally has tracks 103 of an aluminum reflective layer that are formed on a surface of a base 102. Information is recorded on pits and grooves 104 which are asperities finely formed on the tracks. Reference numeral 105 denotes a protective layer.
In a typical optical disc drive shown in FIG. 5, reading is performed on the tracks 103 by a laser beam Ph from a pickup 107 while the optical disc 101 is rotated in the direction of arrow C by a disc motor 106. The pickup 107 is screwed onto a feed screw 109 driven by a traverse motor 108. A servo control circuit 110 drives the traverse motor 108 to move the pickup 107 in the radial direction in such a way that the tracks 103 are traced according to the reproduction output of the pickup 107. Further, the servo control circuit 110 detects address information recorded on the tracks 103 and drives (CLV control) the disc motor 106 with a constant linear velocity.
To be specific, the irradiation position of the laser beam Ph on the optical disc 101 is controlled not only by driving the traverse motor 108 but also by driving a tracking actuator (not shown), which is provided in the pickup 107, to control the position of an optical path of the laser beam Ph in the lateral direction (radial direction) with respect to a surface of the optical disc 101 as necessary; meanwhile, the tracks 103 are traced accurately.
Unlike audio CDs and video CDs, in the case of an analysis disc, an analysis object 111 is further disposed in the optical disc 101 as shown in FIGS. 6 and 7. In an analysis apparatus using the technique of a conventional optical disc drive, light reflected from the analysis object 111 is read by a PD (photodetector) 117 of the pickup 107 shown in FIG. 8 and is processed by a video signal processing circuit 112 to obtain an image of the analysis object 111.
FIG. 8 shows a power control circuit of the pickup 107 shown in FIG. 5.
A laser beam output is emitted from an LD (laser LED) 113 of the pickup 107 to the optical disc 101 to read information written on the pits, grooves, and the like of the optical disc 101 and information for each driving servo. The laser beam output is simultaneously emitted to a front monitor 114 serving as a monitor light-receiving element.
The output voltage of the front monitor 114 is inputted to an APC circuit (Auto power control circuit) 115. The APC circuit 115 operates a laser drive circuit 116 in such a way that the front monitor 114 has a constant voltage, and the APC circuit 115 performs feedback control in such a way that the LD 113 has a constant output. The above analysis apparatus is no exception and similar control is performed therein, which effectively acts on stable capturing of signals from the pits, grooves, and the like on the disc.
In the optical disc drive shown in FIGS. 5 and 8, the LD 113 and the PD 117 of the pickup 107 are provided on one side of the optical disc 101 to process a detection signal of laser light which has been emitted to and reflected from the optical disc 101. A power control circuit for the pickup 107 of an optical disc drive is configured in the same manner as in FIG. 8. In the optical disc drive, the pickup 107 has the optical disc 101 interposed between the LD 113 and the PD 117 as indicated by a virtual line of FIG. 9 to process a detection signal of laser light which has been emitted to and passed through the optical disc 101.
However, an output for capturing on the pits and grooves is not always optimum as a laser output for obtaining an image of the part of the analysis object 111.
This is because a laser path for obtaining information from the pits and grooves provided in the optical disc 101 is different from a laser path for obtaining an image from the analysis object 111.